Controlling phase relations between stations



Dec. 24, 1929. H. NYQuls'r 1740s857 CONTROLLING PHASE RELATIONS BETWEEN STATIONS Original Filed Oct. 19. 1927 z sheets-Sheet l i JNVENTOR.

' ATTom/El Dec. 24, 1929. H. NYQUlsT 1,740,867

CONTROLLING PHASE RELATIONS BETWEEN STATIONS Original Filed Oct. 19. 1927 2 Sheets-Sheet 2 ATTORNEY Astation in a desired phase relation. particularly, the invention has applic-ation to Patented Dec. 24, 1929 Unirse srA'rEs PATENT OFFICE HARRY NYQIST, OF MILLBURN, NEW JERSEY, ASSIGNOR T0 AMERICAN TELEPHONE AND TELElG-R-API-I COMPANY, .A CORPORATIGN OF NEVI YORK CONTROLLING PHASE RELATIONS BETWEEN STATIONS v Application filed etober 19, 1927, Serial No. 227,303. Renewed September 13, 1929.

This invention relates to methods and arrangements for maintaining the current supplied from one station over a line to a distant More maintaining constant phase relations between the carrier waves of a plurality of broadcasting stations transmitting upon the same wave length.

When distant rad-io stations are connected by telephone lines so that they may broadcast the same program, it becomes `desirable that all the stations use the same carrier frequency in order to reduce the number of wavelengths required for the one program.y Such a method of operation, however, encountersthe difliculty that slight changes in the relative phases of the radio frequency currents from'the various broadcasting stations affect the field strength in certain localities, thus causing received signals to Vary in amplitude, and in some cases to vanish completely.

In accordance with the present invention, it is proposed to remedy this condition by supplying a controlling current of some Vbase frequencyI over wire lines to the various broadcasting stations, the common-carrier wave at the various broadcasting stations being derived from or controlled by the base frequency so transmitted. In order to compensate for the variation 1n phase produced upon the controlling or base frequency by reason of temperature or other variations of the line7 a special automatic arrangement is 'Y provided to produce in the line changes to compensate for the changes in phase.

Specically, the present invention conteniplates controlling the phase variation by transmitting the control current from the originating station over a line to a distant station at which the phase variation becomes effective, and thence back over a similar line to the original station. A certain normal difference in phase may then be noted between -the current leaving the original station and the current coming back.' By observing variations in this phase dierence and adjusting phase controlling networks in the outgoing and controlling line to compensate for the observed variation, this current may be maintained at the distant station in a substantially constant phase relation with respect to the originating current source.

The invention may now be more fully understood from the following detailed description thereof when read in connection with the accompanying drawing, of which Figure v1 shows curves illustrating the principles underlying the invention; Figs. 2 and 3 illustrate schematically certain types of radio antennae; Fig. 4 illustrates a circuit arrangement embodying one form of the invention; Fig. 5 is a diagram illustrating the operation of a push-pull detector forming the part of the mechanism illustrated in Fig. 4 ;v and Fig. 6 shows with some degree of detail the controlling mechanism symbolically represented 'in Fig. i.

As a simple illustration of varying field strength let us consider two broadcasting stations symbolically represented at the points designated East and l/Vest in Fig. 1. Each station may be supposed'to have'a 'similar antenna consisting of a vertical rod with equal sources of electromotive force between the rod and the ground.` Under these circumstances, each antenna is surrounded by a magnetic field and an electric field, these fields decreasing in strength with increasing distance from the antenna. Onlya few lines of force are shown in the diagram of Fig. 1 in order to indicate the direction of certain portions of the fields. The lines marked e and e represent lines of force ofthe electric field, the arrows indicating the direction. Similarly, the circles vmarked m and m indicate the lines of force of the magnetic field, entering and leaving the paper in a plane at right angles thereto. The circles with the crosses represent positive lines of force and the circles with the dots in the center represent negative lines of force.

If the urrent in each antenna is in phase, then at the point a midway between the stations the magnetic flux, m, surrounding the east antenna will be equal and opposite in direction to the magnetic fluX, m', surrounding the west antenna. The resultant magnetic field at point a is therefore equal to zero.-

versa.

should differ by 1800, then at a the vectors representing the alternating magnetic fluxes would add, while at b, a point just onequarter Wave length distant from a, the fluxes would subtract. At c one-half wave length to the magnetic field, while the second term is that due to the electric field.

The current flowing in the receiving antenna due to waves from the west station may be represented:

in which A1 and A2 are again magnitude constants, which may have the same or nearly the same values as in the case of equation (l) and 1,//1 and 1,//2 are phase angle constants.

These expressions may be rewritten in thc form of resultant vectors, as fellows:

netic fields m and m are a maximum, Due to their relative directions at point a, however,-the resultant of e plus e is a maximum while that of m plus m is zero. As phase shifts occur, the location of maximum and minimum resultant electrostatic fields is changed.

It is, of course, possible to devise receiving antennae structures which will respond to the magnetic fields without being substantially affectedI by the electric elds, and vice For example, the loop type antenna such asis illustrated schematically in Fig. 2, responds mainly to magnetic fields, while the antenna of the type conventionally indicated in Fig. 3 responds mainly to electric fields. |The ority of antennae, however, such as l o -r T type antenn, are responsive to both magnetic and electric fields.

With these considerations in mind, let us analyze the character of the current received' where the'antenna is responsive to both magnetic and electric fields and located at any given point in the vicinity of a of Fig. l. Assuming the point a lies midway between two similar transmitters, each transmitting through similar media, let m equal the distance from the point a to a receiving station near a; and located on the line c-a of Fig. 1. llso, let equal the wave length oll both oscillators. Then the current flowing in the receiving antenna due to waves :trom the east transmitter is:

ln Equations (3) and (4C) the symbols 02 and :,lf3 have the following values:

A? sin 02 (r) Now, since the phase angle constants in tl ic foregoing equations are functions of the transmitting antennae and the transn'iitting media, which are assumed to he the same for both transmission east and west, it is evident that the expressions cos 02- 6]) and cos (e2-lll) in Equations and will be equal to each other, and hence the terms under the radicals in said equations are equal. It is also evident that L2 plus IW add up to zero whenever All rhpsva: j; mr radians (7) ifa COS (wi-@wipe COS (wl-@+09 1) In the foregoing equation, t is the time of transmission: w is 27: times the frequency; A1 and A2 are magnitude constants; and 91 and 62 are phase angle., constants. Also, the ,first terml of the quantity represented by the right hand side of the equation is the current due or controlled. by the same fundanicntal controlling current (preferably of voice 'Fie qnency) transmitted over a telephone line between the atatias. the phase relation bcrne n i radio currents will be constant, v led the phase relation between the tuncontrolling wave from the source S is transmitted from the radio station at which the transmitter RT is located over a line Ll to the station at which the radio transmit-ter RT is located. In order that the controlling current I2 arriving at the station RT will always have a constant phase relation with respect to the controlling current I1 leaving shift of degrees. Vhen conditions are normal,the adjustment of the lines L1 and L2 is such that the returning current I3 is 90 out of phase with the current I1 leaving the source. S. In order to maintain this phase condition with respect to the currents I1 and I3, and in order to automatically produce the necessary compensating adjustment of the networks PN1 and PNQ, a push-pull detector circuit, comprising detector tubes tand 5, 1s provided, and the input circuits of these i tubes are so arranged that the current I1 from the source S is applied serially to the grids of the two tubes through the transformer l, while the returning current I3-is applied to the grids in parallel through the transformer 1X2 3. Resistances are connected across the plate circuits of the two tubes, and the polar relay PR, for operating the control mechanism (see Fig. 6), is connected across the terminals my.

The operation of the push-pull detector may be understood by reference to Fig. 5. When the voltage El changes from its 90 relation with E3 by an amount 8, the voltage E4 on the grid of oneof the tubes is increased, while the voltage E5 on the grid of the other tube is decreased. Consequently, the rectiiied current in one tube is increased while that in the other tube is decreased. Accordingly, when matched tubes are employed there will result a positive or negative potential between the points and y, depending upon normal 90o relation exists between the currents I1 and I3, there will be no potential drop between the points and y, and the armature of the polar relay PR will be in its neutral position. If the phase varies in one direction, however, the armature of the polar relay is shifted to, say, its upper position, thereby energizing the relay 7 and causing the motor M to be driven in one direction. If the phase variation is in the opposite direction, however, the armature of the. polar relay will be shifted to its lower contact, thereby energizing relay 8 to drive the motor M in the opposite direction. The motor M may be geared by means of any suitable mechanism to simultaneously vary the phase adjusting networks PN1 and PN2.

The control mechanism. illustrated in Fig.- 6 is merely a conventional representation of mechanism capable of carrying out the desired function. It will be understood that any other suitable mechanism well known in the art may be employed for this purpose. Likewise. the variable phase shifting networks PNl and PNZ, which are merely symbolically indicated, will be understood to be any one of the many types of phase shifting mechanism known in the art.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. In a system in which alternating current from a source located at one station is supplied to a translating device located at. a distant station which is connected to the first station by two transmission paths, each having. individual phase controllingy elements, the method of maintaining a constant phase relation between the current at the two stations which consists in transmitting the alternating current from the source at the first station` to the distant station over one. path, transmitting the current incoming at the distant station back to the lirst station over the second path, observing any variation in the normal phase difference between the leaving and arriving currents at said first station, and adjusting the phase controlling elements individual to the two paths so thaty each element compensates for that portion of the observed variation which is due to the phase shift of its path..

2. In a signaling system, an alternating current source located at one station, a translating device supplied with current from said source and located at al distant station, a transmissionA path` over which alternating current from said source is transmitted to said distant station, a path over whiclrcurrent coming at said distant station is transmitted back to said first station, means at said first station for indicating variations in the normal phase difference between the leaving and arriving currents thereat, and adjustable phase controlling networks in each of said paths, each network being adjustable to coinpensate for that portion of the indicated variation in phase difference which is due to the phase shift of its path.

3. In a signaling system, an alternating current source located at one station, a translating device supplied with current from said source and located at a distant station, a transmission path over which alternating` current from said source is transmitted to said distant station, a path over which current incoming at'said distant station is transmitted back to said first station, controlling means at said first station for indicating variations in the normal phase difference between the leaving and arriving currents thereat, adjustable phase controlling networks in each of said paths, and connections between said networks and said controlling means whereby each network will be adjusted to compensate for that portion of the indicated variation which is due to the phase shift of its path.

4. 'In a signaling system, an alternating current source located at one station, a transw lating device supplied with current from said source and located ata distant station, a transmission path over which alternating current from said source is transmitted to said distant station, a path over which current incoming at said distant station is transmitted back to said first station, said paths being normally so adjusted that a phase difference of 90O will exist between the leaving and arriving currents at said first station, controlling means unresponsive to said leaving and arriving currents when a phase difference of 90o exists between them, adjustable phase controlling networks in each of said paths, and connections from said controlling means, to said networks whereby said controlling means will operate when any variation from said 90 phase difference occurs to adjust each network to compensate for that portion of the variation which is due to the phase shift of its path.

5. ln a signaling system, an alternating current source located at one station, a translating device supplied with current 'from said source and located at a distant station, a transmission path over which alternating current from said source is transmitted to said distant station, a path over which current incoming at said distant station is transmitted back to said first station, said paths being normally so adjusted that a phase difference of 90 will exist between the leaving and arriving currents at said first station, a push-pull detector circuit and a polar relay controlled thereby, connections whereby said leaving and arriving currents at said first station may be applied to said push-pull circuit in such relation that when a 90 phase shift exists the armature ot said relay will be in a neutral position, adjustable phase controlling networks in each of said paths, and mechanism controlled by said polar relay to adjust each of said networks to compensate for that portion of any variation from the 90 phase difference normally existing` be tween said leaving and arriving currents which is due to the phase shift of' the path in which the network is located.

In testimonyv whereof, l have signed mname to this specification this 18th day of October, 1927.

HARRY NYQUIST.

ldd 

